1. Field of the Invention
The present invention relates to electronics packaging technology. More specifically, the present invention relates to a three-dimensional ("3-D") multi-chip package that operates in the microwave frequency range.
2. Description of the Related Art
One common application for microwave signals was in the field of radar. In earlier radars, the antenna was in the form of a dish, which was mechanically rotated to perform the scanning function. An exciter generated an RF microwave signal which was transmitted through a travelling wave tube, where the RF signal was then amplified to a high level signal and finally radiated out through the mechanical antenna. Rotating the antenna effectively pointed the signal in various directions in the sweeping mode.
The next generation of radars employed phase shifters, no longer relying on the use of a mechanical antenna that needed to be physically rotated in order to sweep an area. In this design, a fixed antenna array was used, and the phase shifter changed the beam direction by shifting the phase of the RF energy. Accordingly, the device electronically steered the beam out of the antenna array.
In the next generation of radar, a concept called an active array transformed the formerly passive fixed antenna into an active radiating mechanism. In such a radar, a plurality of transmit and receive modules ("T/R module or element") sometimes were arranged on a stick or similar configuration. Each T/R module or element was in fact a transmitter and a receiver for the radar all in one. Usually, the T/R module or element included a transmit chip, a receiver chip, a low noise amplifier, a phase shifter, an attenuator, switches, electrical interconnects to connect the components, and logic circuits that controlled the components.
All of the components were disposed on a single substrate in a package which comprised the T/R module or element, which itself was positioned behind a radiator. The radiators and corresponding T/R modules or elements were deployed in a grid. As is known in the art, the microwave signal was emitted and received through the radiators. Behind the T/R modules or elements was a manifold, which provided input and output of the RF signal to and from the T/R modules or elements. Behind the manifold was where the received RF signals were summed, mixed in a receiver, then digitized and supplied to data and signal processors, from which eventually target information was derived.
Using a stick or similar configuration to assemble and package the T/R modules or elements, which comprised an active array, was very expensive. Also, the stick weighed several hundred pounds. Further, the bulk of the active array was often twelve inches or more in depth. Hence, the conventional active array did not have a low profile and accordingly could not be integrated easily into the skin of an aircraft, a missile, or spacecraft, for example, where space limitations are often critical. Even aboard ships, the moment of inertia of a heavy antenna on a tall mast support must be avoided. Consequently, there is presently a need for a more compact subarray that is easily adaptable to cramped environments such as in a missile, tactical aircraft, spacecraft or ground and ship based radar. There is also a need to reduce the cost of manufacturing active arrays.